Dipole antenna direction finder



Dec. 27, 1949 H. G. BuslGNlEs DIPOLE ANTENNA DIRECTION FINDER I5 Sheets-Sheet 1 Filed April 9, 1945 .o S O J 0 VJ r mw M N N 0 ES v... 1 Vu m J F 5. A a M Y O /l 0W H Y B Z a Zw l 5 l W ya .JJYQW u r T E y m H c M W. a m 1 .M w QNNJS@ www wnx lvurV/l! o Dec. 27, 1949 H, G, BLJQJGJWES 2,492,354

DIPOLE ANTENNA DIRECTION FINDER Filed April 9, 1945 3 Sheets--SheefI 2 ff 6A 5 @@g L 10 I /'L d 5h L`7 Dec. 27, 1949 H. G. BUsIGNlEs DIPOLE ANTENNA DIRECTION FINDER 3 Sheets-Sheet 3l Filed April 9, 1945 KEY/NG CONT #0L INVENTOR. HE/V/ G. 50S/@NAES BY ,il

ATTORNEY Patented Dec. 27, 1949 y UNITED STATES PATENT OFFICE DIPOLE ANTENNA DIRECTION FINDER Henri G. Busignies, Forest Hills, N. Y., assignor to Federal rlelephone and Radio Corporation, New York. N. Y., a corporation of Delaware Application April 9, 1945, serial No. 587,242

Claims.

This invention relates to direction-finding systems and more especially to antenna arrays to produce crossed-field diagrams.

A principal object of the invention is to provide a direction-finding system employing a dipole array wherein certain errors caused by undesired polarization eiects are avoided.

It has been proposed heretofore to employ for direction finding, a so-called elevated H antenna system usually consisting of a pair of substantially parallel elevated dipoles. It has been found that in such systems there exists an error factor caused by the horizontal connecting member which extends between the dipoles. This connecting member has usually been of conducting material, and various proposals'have been made to eliminate the effect of this conductor upon the desired crossed-field diagram. The present invention provides a direction nder employing dipoles or tuned antennae and has for its object employ a central or main receiving antenna and to employ in conjunction therewith a pair of laterally-spaced auxiliary tuned antennae, preferably dipoles. These auxiliary dipoles however are used as localized reradiators to give the desired crossed diagram effect so that the array can be used to determine the bearing and direction of a distant transmitter or radiation source. Merely for purposes of explanation, the auxiliary dipoles will be referred to as free dipoles in that their effect on the direction-finding radio receiver which is connected to the main antenna, is substantially entirely by reason of space induction and radiation from the auxiliary dipoles to the main antenna.

Accordingly,\it is another principal object to provide a direction-finding system employing a main direction-finding antenna in conjunction with a plurality of free dipole antennae for producing a direction nder system of the crossed diagram type.

A feature of the invention relates to a direction finder employing a main receiving antenna unit and a plurality of auxiliary antenna units coupled thereto substantially entirely by space radiation or induction, together with means to render said auxiliary units alternately effective as reradiators in setting up a crossed diagram eld effect.

Another feature relates to a direction-finding system employing a main direction-finding antenna and a plurality of spaced dipoleswhich act as auxiliary radiators 'to the main antenna,

Aeffectively to reduce, if not entirely eliminate, `the above-mentioned undesired polarization ef fect. In achieving this object, it is proposed to 2 the auxiliary radiators being timed and phased so as to produce an equivalent crossed diagram eiect for direction nding.

A further feature relates to a direction finder employing a main receiving dipole with a pair of auxiliary tuned reradiating dipoles and a receiver and indicating system connected to the main dipole. The dipoles are positioned and spaced apart relatively to each other so that the resultant eiiect on the direction-finding indicator corresponds to the bearing and direction of a distant radiation source.

A further feature relates to an improved direc tion finder employing a plurality of free dipoles and which is substantially free from horizontal polarization errors.

A still further feature relates to a novel method of controlling a cathode ray tube oscilloscope to produce visual signals indicating the bearing and direction of a distant radiation source.

Other features and advantages not particularly set forth, will be apparent from the following descriptions and the appended drawing wherein,

Figs. 1 to 4 are rudimentary diagrams used in explaining the invention.

Figs. 4A and 4B are vector diagrams explanatory of Fig. 4.

Fig. 5 is a set of curves to illustrate the timed operation of the reradiating antenna units according to the invention.

Fig. 6 is a resonance and phase diagram useful in explaining the invention.

Figs. '7 and 8 are other schematic explanatory diagrams.

Fig. 9 is a composite schematic diagram of a direction-iindng system embodying features of the invention.

Fig. l0 is a diagrammatic plan view of a modified manner of supporting the auxiliary dipole antennae according to the invention.

Fig. l1 is a schematic diagram of a further direction finding system embodying features of the invention. f

It is known that when a vertical receiving antenna such as the antenna I (Fig. l) is connected to any well-known direction-finding radio receiver 2, and a length of vertical conductor 3 is moved around the antenna in a cylindrical path, negligible effect is produced upon the field affecting the antenna I. This is true when the conductor 3 is short with respect to the wave length of the main field affecting antenna I and when the conductor 3 is detuned with respect to the received frequency. When, however, the conductor 3 is tuned to the received frequency, the effect on 3 antenna I of the auxiliary eld reradiated from antenna 3 is a substantial percentage of the effect produced by the main or primary field on antenna I. If such a tuned conductor is rotated around antenna I, it causes variation of the polar diagram l as shown in dotted outline in Fig. 2. If a similar tuned conductor (Fig. 4) were also rotated around antenna I and tuned in timed relation with respect to conductor 3 so that the two tunings are respectively 180 out of phase, the combined result would be a crossed-eld diagram such as shown in Fig. 3. This would enable the combination to be used as a direction nder. Such an arrangement of main antenna and auxiliary free reradiating antennae has the advantage of substantially eliminating polarizing errors which would unavoidably arise if the auxiliary antennae 3 and 5 were connected by conductors to the antenna I, as is the case in so-called elevated H antennae.

Ordinarily, the conductors 3 and 5 are in the form of dipoles and in accordance with the invention they are tuned in any suitable way as schematically represented by the parallel inductances and capacities connected between their adjacent arms. However, one of the practical diiculties with such an arrangement is that of requiring a high degree of accuracy in the tracking of the tuning of the two auxiliary dipoles. Furthermore this tuning must be effected without using a. conducting shaft or beam extending between the antennae 3 and 5.

In accordance with one aspect of the invention, the two dipoles 3 and 5 are located at the ends of a non-conductive horizontal beam member. When the two auxiliary dipoles are tuned to the frequency being received by the main antenna I, and are located at relatively short distances therefrom, e. g., of the order of 2.5 meters, suf'- cient current will be set up inthe auxiliary dipoles to induce in, and reradiate a eld to, the main antenna I, which eld is ofthe same order of strength as the main or primary field from the distant source whose direction is to be determined. In order to tune the dipoles, an inductance and variable condenser can be connected, as shown in Fig. 4, in each dipole. At frequencies for which each dipole is materially less than one-half wave length, the radiation resistance of each dipole system will be very small, and if high quality reactance elements are used for tuning, the Q of the resonant circuit will be high. In fact, at all those frequencies for which there is a pronounced undesirable horizontal polarization effect in the equivalent elevated H antenna, the Q of each of the reradiating dipoles according to the invention will be fairly high,

e. g., above 20. This relatively high Q causes the tuning of the dipoles to be very sharp. Consequently small variations in values of tuning capacitance cause comparatively large variation in phase angle between voltage and current. That is, there is a large variation in the phase of the primary electric field which acts on each dipole and the electric field reradiated therefrom. In the vicinity of resonance, the phase angle is the arctan lQ-I-C/Co where Ca is the capacitance at resonance. In accordance with one feature of the invention, the resonance of the two reradiating dipoles is controlled so as to minimize the critical eect of the resonance tuning thereof.

It is well-known that a resonant dipole located -in an electric ileld has set up therein a current which is in phase quadrature with the primary electric field acting thereon. This current flow- 4 ing in the dipole is itself a source of electric field which, for purposes of analysis, can be considered to be made up of two components, the reradiation fleld and the inductance field. When the 5 dipoles 3 and 5 are located at a distance approxi- -mating a small fraction of a wave length, the two components are of substantial magnitude, and

therefore the reradiated iield must be considered as made up of space induction and radiation.

Consequently the phase between the primary or main eld acting on antenna I and the field from each of the dipoles 'will vary from 0 to 180.

For purposes of explanation the expression primary field as used herein refers to that field emanating from the distant source whose bearing and direction is to be determined according to the invention.

Let it be assumed for example, that the dipoles 3 and 5 are spaced apart about live meters and each is tuned exactly to resonance with the frequency of the primary field. Then it is possible to determine the total diiference in phase between primary iield and reradiated field by adding tothe actual electrical phase difference between the fields, the difference in space phase corresponding to the distance between each dipole and the main antenna, and also by adding the space phase corresponding to increased length of primary wave path to each dipole in excess of the length of the primary wave path to antenna I when the assembly 3 and 5 is rotated at an angle to the primary wave front. Fig. 4A shows the vector relations when the line joining dipoles 3 and 5 is parallel to the wave front Aof the primary field, and Fig. 4B shows the vector relation when it is at an angle. In each of theseiigures the vector e indicates the primary iield and the vector r represents the reradiated field, and the anglers is the space phase `angle lag above mentioned. In Fig. 4A the amplitude of the demodulated signal in receiver 2 is the sum of the two vectors e and r. In Fig.

4B the amplitude of the demodulated signals is the sum of all the vectors. The resultant phase angle in Fig. 4B is given by (21d/A) sin 0 where d equals the distance from antenna I to each dipole, i is the wave length of the primary field, and 0 is the angle through which the antenna .system has been rotated.

50 In accordance with the invention, special means are provided to determine and produce an indication when the phases of the two reradiated fields respectively from 3 and 5 are equal. The direction of the wave propagation from the distant source can then be determined as perpendicular to the azimuthai angle of the line connecting dipoles 3 and 5 provided, of course, the dipoles are identical and are off resonance by exactly the same amount.

In order to avoid the difficulty of accurate tracking of the tuning of each dipole, a preferred arrangement such as shown in Fig. 9 is employed, wherein the auxiliary dipoles 3 and 5 aresupported on a suitable non-conducting beam indicated by dash line 6A and are tuned each by a fixed condenser 6, I and by an associated adjustable trimmer condenser 8, 5. The rotors or adjusting shafts of condensers 8 and 9 are coupled to a non-conductive rotatable shaft I0. The condensers 6 and 'I are roughly adjusted near the tuning resonance point and the condensers 8 and 9 are arranged to be displaced around a mean resonance value at a low frequency rate, e. g. twenty or fifty timesper second under control of shaft I0 which is driven by a suitable motor Il.

In order to produce the eiect of alternating switching in and out of the antennae 3 and 5, each antenna is arranged to be tuned to resonance at approximately 180. lag with respect to the other. Fig. 5 shows graphically the rate and timing of the variation of the condensers 8 and 9, curves 8A and 9A, and blocks R3 and R5 represent the effective phase periods of the two dipoles. It will be notedV from Fig. 5 that the conequivalent to a corresponding spacial displacement of the antennae 3 and 5 as represented for example in Figs. 'I and 8. Fig. 'l represents diagrammatically the equivalent apparent displacement of antennae 3 and 5, when the beam of the direction-finding antenna array is perpendicular to the wave front from the distant source; while Fig. 8 represents the equivalent apparent displacement when the antenna array is parallel to the wave front. Near the null point this apparent displacement is analogous to the displacement used in an ordinary cross loop direction finder. It will be seen that by suitable design of the electric parameters, the apparent displacements X to X', and Y to Y', can be larger than the actual physical spacing between antennae 3 and 5. The electric spacing between antennae 3 and 5 may be between 25 and 120.

If the electric spacing between the antennae 3 and 5 is of the order of 90, that is a quarter wave fiecting plates I1 and I8, may be employed. The 50 plates I5 and I6 are energized at the desired horizontal sweep rate, for example by means of a saw-tooth wave generator I9, which is operated or controlled preferably at twice the rate of rotation of a shaft I0. Thus, the cathode-ray beam will pass through one complete horizontal sweep cycle for each resonant tuning period (R3, R5,-

Fig. 5), corresponding to the reradiation from antennae 3 and 5.

The main antenna I is excited by the resultant energy derived from the primary eld and by the energies reradiated alternately from antennae 3 and 5. A suitable radio receiver 20, such as is generally used in radio direction nders, is connected to antenna I and is preferably of the superheterodyne type. The first detector 2| of the receiver feeds a phase discriminator 22 of any well-known type such as' disclosed. The discriminator 22 feeds a second detector 23 whose output is applied across the vertical deilector plates I1 and I8.l

When the antenna array I, 3, 5, is not aligned perpendicularlyto the transmitting source, the energies reradiated by dipoles-3 and 5 will be out of phase with respect to each other. Accordingly,

the signal, after passage through the discriminator 22, will vary in amplitude in accordance with the relative phase displacements of the reradiations. This diierence in phase will appear on the screen of the oscilloscope I4 in the form of two traces TI, T2. 0n the other hand, when the antenna array is adjusted perpendicularly to the distant source, the two traces TI, T2, coincide and appear as a single trace T3. It will be clear that the invention is not limited to the particular type of trace that is produced on the oscilloscope screen. For example, instead of relying upon a coincidence of the two traces to indicate a null point, a xed cross-point on the screen may correspond to the null point, and when the two traces pass through this point, it is an indication that the null position is reached. Therefore, the trace can be used to show the phase variation of the high frequency signals from the distant transmitter as a function of the scanning, or time rotation of condenser-s 3 and 9; and also as a function of the position of the direction-dnding beam which carries the antenna array.

While in the foregoing the free dipoles have been described as being preferably effectively switched-in under control of the 180 displaced resonance tunings,` it will be understood that any other well-known switching method may be employed. For example, in Fig. 11, each dipole 3. 5 may be provided with an individual switch 24, 25 and the switches may be alternately opened and closed at the required rate. These switches will then be controlled from a keying control means 26 by a. non-conducting control such as rotatable Bakelite rods 21, 28. Synchronized with the switching mechanisms is an indicating mechanism which will cause the amplitudes of the demodulated signals to be indicated separately when each of the dipoles is reradiating. The cathode-ray'tube oscilloscope 29 is provided with a switch 30 coupled alternately between ground and a potential source 3l in synchronism with operation of switches 24 and 25. The length oi' these traces are determined by the signal output from receiver 20 proportional to the amplitudes of the demodulated signals when each of the dipoles is reradiating. The signals of different amplitudes are converted into signals of corresponding different lengths in converter 32, which may be of any known form, such as resistant capacity time control circuits. The switching in converter 32 is likewise controlled by keying control 25 through means 33. These output voltages are applied to a control grid 34 rendering the beam vis- 5 ible for a length of time depending upon the signal duration. When the fields of the two dipoles are in equal phase. the primary field or the distant transmitter would have added to it, alternately, two fields which are lagging by a certain angle as mentioned above. Rotating the dipole array about a perpendicular axis will then cause one reradiated eld to lag by a smaller angle, and the other by a, larger angle,'resulting respectively in a smaller and larger amplitude of the demodulated signal. 'I'he effect on amplitude of the demodulated si al by change of phase lag is most pronounced when the reradiated field lags the primary 'field by approximately 90. At frequencies when the lag is too far from 90, the two dipoles 3 and 5 can be equally detuned to change the phase relationship between current and voltage. As shown in Fig. 4B, the effect on demodulated signal amplitude is greatest when the angle between primary and reradiated ields is near 90.

In order to permit operation over a wide band amm 9 and non-conductive means for operating the trimmers in unison so as to tune the associated dipoles approximately in opposite phase a predetermined amount on either side of a mean resonance value.

11. The method of determining the direction from a point of observation to a source of energy radiation which comprises directly receiving energy from said source, setting up a source of energy reradiation in a direction other than that of said first named source, and comparing 'the eiect produced at said point of observation by phasal relations between the direct received cnergy radiated from said first source with that produced by the energy reradiated from said second source.

12. The method of determining the direction of a source of wave radiation which comprises collecting at a given location directly waves from said source, reradiating at one or more points adjacent said location and mixing with said collected waves waves received also from said source, adjusting the phase relation between the directly collected waves and the reradiated waves, and producing therefrom a determination of any phase relation in a given range between said waves as indicative of direction.

13. The method according to claim 12, wherein the reradiation takes place at two points and the reradiated waves are oppositely phased.

14. The method according to claim 12, where-t in the phase relations between the mixed waves is intermittently controlled.

10 15. 'I'he method of determining the direction of a source of wave radiation which comprises collecting at a given location directly waves from said source, reradiating VVat one or more points adjacent said location and'mixing with said collected waves waves received also from said source, adjusting the phase relation between the directly collected waves and the reradiated waves, and producing therefrom a determination of any phase relation in a given range between said waves as indicative of direction, the reradiation taking place at two points and the reradiated waves being oppositely phased, and the phase determination taking place when the phase between waves directly collected and those received for reradiation is equal.

HENRI G. BUSIGNIES.

REFERENCES CITED The following references are of record in the iile of this patent:

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